1. Field of the Invention
The present invention relates to an IC socket of a zero insertion force (hereafter, ZIF) type.
2. Description of the Prior Art
There is an increasing demand for multi-functional and compact electronic equipment. In an effort to realize such electronic equipment, a surface mounting technique has been widely adopted, and pins of an IC device are arranged with smaller pitches or increasing in number, and IC devices are now designed to be more compact or have pins with smaller pitches, thereby resulting in shorter lead pins of an IC device. These lead pins are easily deformed and the compact sockets provide less contact area.
When a burn-in test or other test is performed on an IC device, a ZIF-type IC socket having contacts capable of opening and closing is employed so that no force will be applied to the lead pins of the IC device when the lead pins are inserted.
FIG. 8 shows an example of a conventional ZIF-type IC socket (disclosed, for example, in Japanese Utility Model Unexamined Publication No. 2-28624). The IC socket has holes 2 on the surface of a socket body 1. Lead pins of an IC device are inserted into the holes 2 as indicated with arrows. The holes 2 have contacts for receiving the lead pins. Each of the contacts is made up of a first contact element 3 that is fixed and a second contact element 4 that is elastically deformable. Lead pins are inserted between the first and second contact elements 3 and 4, and then locked.
An actuator 5 is installed to open or close the contacts. In the prior art shown in FIG. 8, the actuator 5 is formed with a movable plate arranged on the surface of the socket body 1, and has engaging means 6 that engage with the tops of the second contact elements 4. When lead pins are inserted, the actuator 5 is moved left. Then, the second contact elements 4 are moved left accordingly. Thereby, openings are created between the second contact elements 4 and the first contact elements 3. The lead pins are inserted smoothly without being subject to applied forces by the contacts. When the lead pins are inserted into the contacts, the actuator 5 is moved right. Then, the second contact members are moved right and reset to the original positions. Eventually, the lead pins are held between the first and second contact elements 3 and 4.
FIG. 9 shows another example of a conventional ZIF-type IC socket. The IC socket has holes 2 on the surface of a socket body 1. Lead pins of an IC device are inserted into the holes 2 as indicated with arrows. The holes 2 have contacts for receiving the lead pins. Each of the contacts includes a first contact element 3 that is fixed and a second contact element 4 that is elastically deformable. The lead pins are inserted and held between the first and second contact elements 3 and 4.
In the prior art shown in FIG. 9, an actuator 5 is formed with a movable plate arranged inside the socket body 1 having an engaging means 6 for pressing the second contact elements 4 towards the first contact elements 3. The actuator 5 is pressed leftward by a cam 7. When lead pins are inserted, the actuator 5 lies at a position as illustrated. Openings are created between the second contact elements 4 and the first contact elements 3. The lead pins are inserted smoothly without being subject to applied forces by the contacts. When the lead pins are inserted into the contacts, the cam 7 is rotated in the arrow direction to move the actuator 5 to the left. Then, the second contact elements 4 are moved towards the first contact elements 3. The lead pins are held between the first and second contact elements 3 and 4. In FIGS. 8 and 9, the first and second contact elements 3 and 4 are connected to a circuit board.
In the prior art shown in FIG. 8, an actuator 5 is arranged on the surface of a socket body 1 so that engaging means 6 will engage with the upper ends of second contact elements 4. This increases the depths from the surface of the actuator 5 to the contact points between the second contact elements 4 and the lead pins. Therefore, the IC socket of the prior art cannot apply to an IC device having shorter lead pins. In particular, IC devices to be mounted by surface mounting are usually required to be compact in design, and, therefore, have shorter pins. The IC socket of the prior art shown in FIG. 8 is unusable for these IC devices.
In the prior art shown in FIG. 9, the contact points between second contact elements 4 and lead pins can be positioned in the vicinity of the surface of a socket body 1. This IC socket can apply to an IC device having shorter lead pins. However, the contacts of the IC socket are the normal open type. After the lead pins are inserted, an actuator 5 must be moved to the left and held at a position so that the lead pins can be held between the first and second contact elements 3 and 4. In this way, electric continuity is ensured. The socket body 1 and actuator 5 are resin molded. This means that the socket body 1 and actuator 5 have been loaded. When heating in a burn-in test, the resin creeps to weaken the contact forces between the lead pins and the first and second contact elements 3 and 4.
The purpose of the present invention is to provide an IC socket having contacts capable of being applied to an IC device having short lead pins that are designed for high-density mounting and ensuring reliable contact with the lead pins during use thereof.